know that he had been at least an occasional tutor/mentor to Faramir. And I would venture probably many other young princes of Gondor and Arnor if they were receptive.

Yes, that was what I was referencing, though Arnor had already broken up into the three smaller kingdoms of Arthedain, Cardolan and Rhudaur by the time Gandalf came to Middle-earth. Still, he surely had some sort of interactions with the Dúnedain of the North Kingdoms. We don't really know what Gandalf attempted to do about the rise of Angmar and the Witch-king's assaults on his neighbors. "Change is inevitable. Growth is optional." - DRWolf (after John C. Maxwell)